I'm a bit confused about this. I can't be sure, but it seems from the quote in the article that Tim Willits is referring specifically to the networking aspect of the games.

"We never released Doom 1 and Doom 2 on the PlayStation Network. So we're like, 'OK, what's the easiest way to do this?' And what the guys did instead of rewriting all the network support, [support for] friends, and all that kind of stuff, is they took Rage, took out all the 'Rage' bits and put Doom 1 and 2 on top of it."

Like I said, I can't be sure, I could be wrong. In any case, the article also says the games will be identical to their original versions. And that's pretty much common sense. Any changes to them would be met with fan backlash. Hell, Carmack got backlash when he modified the look of the pistol in Wolfenstein for the iPhone verson, so I doubt they'd change anything here.

It would be interesting to see how the games will run with the idtech 5 engine...I hope. I might get it just out of curiosity, but seriously, using Rage's engine? Why not just use a more reasonable engine?

It will probably be an interactive texture like that Doom 3 mod that allows playing Doom inside Doom 3. The gory stuff like most of Doom's game logic will probably reside in a binary blob or VM of sorts, and the only rewritten portion will be the part where network I/O and peer-to-peer hosting is performed: those aspects will somehow be packaged in a format the Rage engine understands ("move data blob X from interactive surface A to surface B over the network")/

Certainly, that's much easier to do than e.g. making an automated IWAD converter to RAGE format and hacking the Rage engine to display 2D sprites and try to recreate all of the Doom engine's quirk with scripting. Still....what they won't do for a buck.

You've gotta pay Microsoft a bazillion ton of money in order to put anything -- even a bugfix patch -- on the Xbox downloady thingy. Which is why you only put free stuff here if you absolutely need to (like bugfix patches).

A netcode DLC for an old game like Doom 2 would never be profitable enough to be worth the attempt.